3
$\begingroup$

For a model aircraft designed for cruise at say 0.75 Mach, do delta wings offer any benefit over straight wings. Is drag saving from elimination of the tail large enough to consider a delta configuration?

$\endgroup$
1
  • $\begingroup$ Does "straight" mean "non-swept"? Question would be improved by editing to clarify this-- as far as I can tell, all answers posted so far are actually comparing delta wings to swept wings. Suggested edit: in body of question replace "straight wings" with "straight (non-swept) wings". I'm not 100% sure that this is the actual intent of questioner so will leave it up to him/her-- $\endgroup$ Dec 18, 2021 at 18:47

2 Answers 2

4
$\begingroup$

Delta wings were studied in the early jet age for use in passenger planes but lost out to the conventional configuration. Avro in Great Britain studied a civilian version of their Avro Vulcan bomber. It was called type 722 Atlantic and could not compete with conventional designs. The tail drag of a conventional design is small when compared to the additional friction drag of the much larger wing area of a delta.

A tailless delta will need a much larger wing area for the same landing speed and have higher induced drag in cruise due to the shorter wingspan. This is slightly offset by a much better structural efficiency of the delta wing, so the empty weight of a delta airplane is much lower than that of comparable conventional designs. If ease of construction is important, the delta is far superior to a conventional design because it will not have the complex high lift devices which help the conventional design to get away with much less wing area.

Deltas shine in other areas: Their low lift curve slope makes them much better for low level flight because gusts result in smaller load factors. This is ideal for low level penetration of air defenses, but that is hardly something a passenger jet is used for. If you want to fly your model at low level and Mach 0.75, go with the delta wing. In dense air and at high speed, induced drag is minuscule, so that disadvantage of the delta falls away.

If you want to include flying wings in the comparison: A tailless straight wing at Mach 0.75 is a poor choice. There is little to compensate for Mach tuck in an overspeed event and the reflex airfoil is pretty much the opposite of what works well in transsonic flow, which is supercritical airfoils. The delta wins hands down. Its structural efficiency allows the use of thin airfoils and vortex lift gives it agreeable landing speeds even without the use of flaps.

$\endgroup$
3
  • $\begingroup$ The question refers to a conventional configuration with straight wing $\endgroup$
    – Abdullah
    Dec 18, 2021 at 0:49
  • $\begingroup$ @Abdullah yes, I'll edit the question $\endgroup$
    – Mridul
    Dec 18, 2021 at 3:56
  • 1
    $\begingroup$ @Abdullah ... and I edit my answer. $\endgroup$ Dec 18, 2021 at 6:01
1
$\begingroup$

The term "model" is one item preventing a resounding NO, but other wise evidence is strongly against the proposal.

The British V-bomber program of the 1950s produced 3 designs for high subsonic, long range (cruising) applications, the Vickers Valiant, the Handley Page Victor, and the delta Avro Vulcan. The US had its similarly sized Boeing 707.

In terms of range, the delta Vulcan fell far short of the others. Amazingly, the best design for cruising was not the 707, but the Handley Page Victor! Politics, poor planning, lack of funds, and poor execution resulted in this advanced subsonic design being relegated to military use.

During operation Black Buck, it was the Victors who refueled the Vulcans on their way to the Falklands and back. The greater strength of the Vulcan delta and its supersonic capability kept it in service longer, but it was the "ugly duckling" Victor design, with its cranked wing and wing root/fuselage jet engine air intakes, that could have given the 707 a run for its money.

The obsession of modern designers to save drag by eliminating tail volume makes about as much sense as a car saving weight by eliminating the steering wheel.

Trusting that a high subsonic "model" would have a Reynolds number greater than 10$^6$, the Handley Page or 707 design may be a good place to start. For a slightly lower Mach specification, such as 0.55, a (relatively) tiny straight wing, such that seen on the DeHavilland Canada Dash 8 turboprop, will give best results for cruising, with traditional slats and flaps for landing.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.